Patrick R. Burns, DPM, FACFAS

Similarly symptoms xanax treats generic risperidone 2 mg online, lithium treatment was associated with increased levels of parathyroid hormones in patients (McKnight et al medications such as seasonale are designed to 2 mg risperidone order visa. Physiological Effects the main physiological role of the parathyroid gland is to control circulating calcium levels (Capen and Rosol xanthine medications purchase 3 mg risperidone amex, 1989; Capen medicine 4211 v purchase risperidone without prescription, 2001) medications known to cause seizures purchase risperidone 3 mg fast delivery. Given the importance of maintaining normal levels of circulating calcium, multicellular organisms have evolved a complex system of controls to ensure this constancy. Vitamin D is produced from precursors in the skin, and it is obtained from the diet (Capen, 2001). Bone is remodeled continuously during adulthood by the resorption of old bone by osteoclasts and the subsequent formation of new bone by osteoblasts. These two events are responsible for renewing the skeleton, while maintaining its anatomical and structural integrity. Under normal conditions, bone remodeling proceeds in cycles in which osteoclasts adhere to bone and subsequently remove it by acidification and proteolytic digestion. Shortly after the osteoclasts have left the resorption site, osteoblasts invade the area and begin the process of forming new bone by secreting osteoid (a matrix of collagen and other proteins), which is eventually mineralized (Capen, 2001). In turn, this demineralizes bone and releases calcium from the bone into circulation (Capen, 2001). Further, it inhibits the renal reabsorption of phosphate, which aids in increasing the solubility of calcium. Vitamin D3 (cholecalciferol) is a steroid-like compound that is essential for calcium absorption in the gastrointestinal tract. It is derived from cholesterol, and the active form is produced from a precursor 7-dehydrocholesterol. Exposure of the skin to ultraviolet light causes formation of vitamin D, which is biologically inert and must be activated by two sequential hydroxylations (Capen, 2001). The hallmark of this disease is abnormally increased bone resorption, leading to severe bone pain. This condition leads to a very densely calcified skeleton, hypocalcemia, and hyperphosphatemia. Of great concern is that hypoparathyroidism often leads to tetany and death (Capen, 2001). The acinar or exocrine portion of the pancreas is concerned primarily with the regulation of gastrointestinal function. Scattered among the pancreatic acini are the endocrine units of the pancreas, the Islets of Langerhans. The major physiological function of the endocrine pancreas is to serve as the primary homeostatic regulator of fuel metabolism, particularly circulating glucose. Islet cells are sensors of glucose homeostasis (maintaining balance by regulation and counterregulation) that respond to changes in their nutrient and hormonal environment. Three major cell types within the endocrine pancreas are known to produce the hormones involved in this regulation. The most abundant cell type is the beta cell, the site of synthesis and secretion of insulin. Glucagon is produced by the alpha cell and the delta cell is the site of somatostatin synthesis. It is likely that a functional relationship exists between the various cell types of the islets because it is known that both glucagon and somatostatin affect insulin secretion, and that somatostatin also influences glucagon secretion. The cells in the parathyroid gland, kidney, and other cells that respond to calcium possess recognition sites for circulating calcium levels known as calcium sensors or receptors. Recently, the calcium sensor or calcium receptor on the parathyroid cell was cloned and determined to belong to the 7-transmembrane class of G protein­coupled receptors linked to phospholipase C. The liver provides most of the circulating glucose in the fasting state by glycogen breakdown (glycogenolysis) and de novo synthesis (gluconeogenesis). Substrates for gluconeogenesis are provided by adipose tissue (glycerol from triglyceride breakdown) and muscle (amino acids from protein breakdown). Specifically, insulin functions to lower blood levels of glucose, fatty acids, and amino acids and to promote their conversion to the storage form of each: glycogen, triglycerides, and protein, respectively. In addition, an increase in the concentration of amino acids (especially arginine and leucine) and ketone bodies in blood also increase the rate of secretion of insulin. Glucagon and the gastrointestinal peptides gastrin, secretin, and gastric inhibitory polypeptide also stimulate release of insulin. The variety of physiological responses to insulin include (a) increased cellular glucose uptake (in most tissues), (b) lower blood glucose levels, (c) stimulated glycogen synthesis (liver, muscle), (d) stimulated glycerol production (adipose tissue), (e) increased amino acid uptake (liver, muscle), (f) inhibited lipolysis (adipose tissue), and (g) stimulated protein synthesis (replication, transcription, and translation), a mitogenic response. As regards the pathophysiology of insulin, hypersecretion produces hypoglycemia and hyposecretion produces diabetes mellitus. Glucagon Glucagon is the primary hormone with action counterregulatory to insulin, because it stimulates catabolic processes (energy mobilization) to prevent hypoglycemia. The most powerful physiological stimulus of secretion of glucagon is reduced circulating blood glucose. Thus, as blood glucose levels fall (hypoglycemia), glucagon secretion increases in an attempt to restore normal homeostasis. In addition to circulating levels of glucose, glucagon secretion is regulated by other factors. The physiological responses to glucagon occur mostly in the liver with a stimulation of glycogenolysis, gluconeogenesis (conversion of amino acids and glycerol to glucose), lipolysis, and ketogenesis (over a long time). Due to the ability of other counterregulatory hormones (epinephrine, growth hormone, and cortisol) to compensate for a deficiency of glucagon, there are no significant pathological conditions associated with abnormal glucagon secretion. Many substances that influence insulin secretion also affect glucagon secretion but usually in the opposite direction. Insulin and glucagon exert opposing effects on various metabolic processes (Table 20-4). Therefore, many investigators like to think of the insulin-to-glucagon ratio in blood as an important determinant of the overall metabolic status. Thus, when there is a high ratio of insulin to glucagon, the effects of insulin dominate, producing a relatively anabolic state. Type 1 (insulin-dependent) results from autoimmune-based destruction of pancreatic cells. Interactions between insulin and glucagon secretion as regulated by circulating glucose levels. Glucose metabolism somatostatin Somatostatin was first isolated from the hypothalamus; its role in regulation of neuroendocrine function is to inhibit secretion of growth hormone in the anterior pituitary. After its identification in hypothalamic tissue, somatostatin was found in other cells of the brain, in various parts of the gastrointestinal tract, and in the cells of the pancreas. The generalized function of somatostatin appears to be as a hormone release inhibitor. Its physiological role within the pancreas is unknown; however, it inhibits secretion of insulin and glucagon (paracrine effect), and inhibits its own secretion (autocrine effect). There is a genetic component associated with diabetes; however, studies in identical twins have suggested there is also most likely an environmental component to the disease. Diet, viral disease, and exogenous chemical substances are thought to trigger a genetic predisposition to its development (Fischer, 2010). This results not only from lack of insulin action, but increased glucagon secretion (which is insulin-dependent in pancreatic cells). Further, the clinical consequences of insulin deficiency are physiologically more severe than those that would result from glucagon deficiency because the other counterregulatory hormones that oppose insulin action can compensate for reduced glucagon regulation. For those reasons, there is relatively little information about chemicals that affect or cells; thus, this section will focus mainly on -cell effects. Both of these selectively destroy pancreatic cells, thereby causing insulin insufficiency (Pisarev et al. Each of these, however, can produce -cell destruction following a single intraperitoneal injection. Isolated intact pancreatic islets synthesize and secrete insulin in response to high glucose (Fischer, 2010). A short exposure of isolated pancreatic islets to alloxan eliminates glucose-stimulated insulin secretion. Furthermore, pancreatic islets have been shown to be deficient in the important protective factor, glutathione peroxidase (Malaisse et al. Decreased insulin (type 1) or insulin action (type 2) inhibits glycogen, lipid, and protein synthesis. Increased glycerol and amino acids serve as substrates for gluconeogenesis to further increase circulating glucose. Diabetes mellitus summary Liver = overproducer of glucose · Increased glycogenolysis · Increased gluconeogenesis * a. Because of increased glycogenolysis and gluconeogenesis stimulated by increased glucagon, the liver becomes an overproducer of glucose. High circulating glucose levels exceed the renal threshold and glucose spills into the urine. In type 2 diabetes, insulin levels also eventually drop due to extended stress placed on pancreatic cells. As a result of the insufficient physiological insulin action, reduced glucose removal from plasma causes hyperglycemia and a variety of metabolic alterations result. The major clinical effects in poorly controlled diabetes usually relate to progressive deterioration of function in a variety of tissues. Diabetes mellitus constitutes a major public health issue with a worldwide prevalence projected to become 366 million individuals by the year 2030 (Lee et al. Thus, morbidity and mortality resulting from this disease make diabetes among the most costly of 998 these combined treatments, several months later the animals exhibit islet cell tumors (Yamagami et al. There is a progressive series of changes involving infiltrating lymphocytes and macrophages in the islets, which produce inflammatory destruction of cells 10 to 15 days after the initiation of treatment (Like et al. Diabetic rats fed a diet supplemented with Coccinia indica fruits or leaves showed renoprotective effects as well as an improvement in glucose tolerance (Gurukar et al. Human -cell destruction has been demonstrated with the rodenticide Vacor (Prosser and Karam, 1978) and during treatment with the drug pentamidine (Bouchard et al. In Vitro Testing Several cell lines are available for testing of insulin secretion. This study showed that hydrogen peroxide produced by these cytokines reacted in the presence of trace metal Fe++ with nitric oxide to form highly toxic hydroxyl radicals. The authors concluded that pro-inflammatory cytokine-mediated -cell death is due to nitro-oxidative stress-mediated hydroxyl radical formation in the mitochondria. However, a potential cytotoxic effect of etoposide on pancreatic cells has also been seen (Lee et al. These findings indicate a potential for this treatment to produce unwanted diabetogenic side effects. A number of proapoptotic mitochondrial and cytosolic markers were investigated and found to be elevated during -cell toxicity. The iAs-induced apoptosis and its cellular signaling events could be reversed by the antioxidant N-acetylcysteine. Reactive oxygen species derived from glucose metabolism provide a metabolic signal for glucose-stimulated insulin secretion from pancreatic cells. Exposure of these cells to low levels of iAs increased an antioxidant-mediated response, and dampened glucose-stimulated insulin secretion. These findings support that low levels of arsenic can induce a cellular adaptive oxidative stress response, and disrupt -cell function. The apoptotic as opposed to oxidative stress effects of iAs between these two studies seem to be disparate. However, two different cell lines were used, and the former study incubated the cells with higher levels of iAs (2 and 5 M), compared with the latter (0. It is possible that oxidative stress induced at the higher levels of iAs exposure (causing cell death) is sufficient to overwhelm that which, at lower levels, plays a regulatory role in insulin secretion (inhibition). This observation suggests that the nature of the cellular response depends on the level of exposure. Glucocorticoid treatment induces insulin resistance and enhances insulin secretion in rodents and humans (Rafacho et al. In that study, dexamethasone treatment of rats for 5 days resulted in hyperinsulinemia at the end of dosing, whereas 10 days following cessation of dexamethasone treatment hyperinsulinemia and insulin resistance had resolved. This provides important information as regards the therapeutic use of glucocorticoids in humans. In a study investigating nondiabetic residents living near a deserted pentachlorophenol and chloralkali factory in Taiwan, insulin resistance was associated with increased circulating levels of dioxins and mercury (Chang et al. Furthermore, increased levels of dioxins and mercury combined were associated with even greater insulin resistance. Thus, simultaneous exposure to dioxins and mercury appears to enhance the risk of insulin resistance. Further, male offspring of the exposed mothers, at 6 months of age, demonstrated reduced glucose tolerance and increased insulin resistance. Effect of maternal nicotine/thiocyanate exposure during gestational period upon pituitary, thyroid and parathyroid function/morphology of 1-month-old rat offspring. Prenatal exposures of male rats to the environmental chemicals bisphenolA and di(2-ethylhexyl) phthalate impact the sexual differentiation process. Toxicity and carcinogenicity of rotenone given in the feed to F344/N rats and B6C3F1 mice for up to two years. Suppression of the brain­pituitary­testicular axis function following acute arsenic and manganese co-exposure and withdrawal in rats. Streptozotocin causes pancreatic beta cell failure via early and sustained biochemical and cellular alterations. Bisphenol A exposure during pregnancy disrupts glucose homeostasis in mothers and adult male offspring.

Ceruloplasmin is a ferroxidase enzyme that is the major coppercarrying protein in blood and helps convert ferrous iron to ferric iron medications 1040 cheap 4 mg risperidone fast delivery, which then binds to transferrin medications heart disease risperidone 2 mg buy without a prescription. Chaperones are also responsible for delivering metals into metalloproteins medications vitamins effective 3 mg risperidone, such as the approximately 1000 Zn and many Cu-containing enzymes in humans (Kambe et al medicine you cant take with grapefruit order risperidone 3 mg visa. As discussed above symptoms low blood pressure 2 mg risperidone buy fast delivery, the 30 zinc channels and transporters chaperone zinc across membranes and through specific cellular compartments. There are many other examples of similar chaperones for essential metals and these chaperones are again a target of toxicity if they are overwhelmed by a competing metal or bind an incorrect metal. Examples include systems to keep redox active iron, manganese, and nickel from damaging organelles and cells (Aguirre and Culotta, 2012). Metallothioneins are an important class of metal chaperones whose expression is induced by metal exposure and that play an important role in essential metal homeostasis and metal detoxification (Isani and Carpene, 2014). Twenty of the 60 amino acids in the metallothioneins are highly conserved cysteines essential for binding and coordinating Zn and Cu, as well as Cd, Mg, and any other d10 electron configuration metals (Isani and Carpene, 2014). Other stimulants include oxidative stress, heat shock, and exposure to chemotherapeutic agents. The high induction of metallothioneins in the kidney by Cd creates a sink for sequestering Cd, such that its biological half-life in humans approaches 30 years. However, this is also the source of renal toxicity when Cd overwhelms the sequestering chaperone. In general, the actions of metals cannot be accounted for by stochastic molecular interactions and instead rely on specific protein binding and coordination in highly structured three-dimensional protein binding sites. With essential metals, the binding and coordination result in enzyme catalytic sites capable of efficient shuttling of electrons. As seen with the metallothioneins, many of the metal ions have great affinity for cysteines, although the metals differ in their affinity to monocysteine thiols, as seen with orthovanadate and organic arsenicals, and cysteine or cysteine/histidine coordination pockets, as with zinc and trivalent inorganic arsenic (Beyersmann and Hartwig, 2008). The valence, charge structure, radius, and physical properties all contribute to specificity in binding. Excretion of Metals Metals are excreted through fecal, biliary, and urinary elimination, as well as through sweat and storage in hair and nails. Several metals including lead, cadmium, arsenic, inorganic mercury, organic mercury, iron, manganese, magnesium, chromium, zinc, copper, nickel, cobalt, tin, and aluminum are excreted through bile and urine with variability to the amount of metals excreted through either route (Ishihara and Matsushiro, 1986). As discussed above, factors that affect excretion of metals include induction of methionine and chaperone proteins (Jaw and Jeffery, 1989). Essential calcium is suggested to decrease bone deposition of lead and invariably increases its excretion and deposition to other target organs (Gochfeld, 1997). In contrast, highly soluble metals that have low protein affinity, such as inorganic arsenic, urinary excretion is the main route of bulk excretion. Metals, such as cadmium, lead, and mercury, are known to be excreted through the skin where the excretion rate might be higher than urinary excretion (Sears et al. Hair and nails sequester metals in keratin matrices to reduce toxicity, and this provides important media for monitoring long-term exposure to metals (Laohaudomchok et al. Biomarkers of Metal Exposure Biomarkers of exposure, toxicity, and susceptibility are important in assessing the level of concern with metal intoxication. Exposure biomarkers, such as concentrations in blood urine, nails, and hair, have long been used for metals. Techniques in molecular toxicology have greatly expanded the possibilities for biomarkers. The capacity for expression of genes that potentially play protective roles against metal toxicity, such as metallothioneins and hemeoxygenase, shows promise as markers of both effect and susceptibility. The use of such biomarkers may aid in identifying particularly sensitive subpopulations. Estimates of the relationship of exposure level to toxic effects for a particular metal adhere to the fundamental principles of dose­response relationships. However, the dose of a metal is a multidimensional concept and is a function of time, as well as concentration. The most toxicologically relevant definition of dose is the amount of active metal within cells of target organs. The toxic form is often presumed to be the free metal, but free metal concentrations are technically difficult or impossible to precisely determine in vivo. In addition, protein binding of metals produces biological effects and the kinetics of binding and sequestering of metals is also very difficult to quantify. A critical indicator of retention of a metal is its biological halflife, or the time it takes for the body or organ to excrete half of an accumulated amount. The biological half-life varies according to the metal as well as the organ or tissue. For example, the biological half-lives of cadmium in the kidney and lead in the bone are 20 to 30 years, whereas half-lives for some metals, such as arsenic or lithium, are only a few hours to days. The half-life of lead in the blood is only a few weeks, as compared with the much longer half-life in the bone and other tissues. As mentioned, hexavalent chromium is predominantly a lung carcinogen due to its kinetics of uptake and retention in the lung epithelium (De Flora, 2000; Park et al. After inhalation of mercury vapor, at least two half-lives describe the retention in the brain, one on the order of a few weeks and the other measured in years. Differences in distribution and retention half-lives greatly complicate the selection of the optimal matrix for assessing functional lead levels (Barbosa et al. The blood, urine, hair, and nails are the most accessible tissues for quantifying metal exposure. The hair and nail content should be considered excreted metal as it is irreversibly sequestered away from biological action. Results from single measurements may reflect recent exposure, long-term, or past exposure depending on retention time in the particular tissue. Blood and urine concentrations usually, but not always, reflect recent exposures and correlate with acute adverse effects. An exception is urinary cadmium, which may reflect kidney damage related to renal cadmium accumulation over several decades. The hair can be useful in assessing variations in exposure to metals over the period of its growth. Analyses can be performed on segments of the hair, so that metal content of the newest growth can be compared with past exposures. For most other metals, however, the hair is not a reliable tissue for quantifying exposure because of metal deposits from external contamination that complicate analysis. However, often only total metal levels can be quantified in nails and it is not possible to identify different metal and metalloid species. This is important for exposures to environmental metalloids, such as arsenic, that are found in many different forms and are metabolized in the body. Chemically, metals in their ionic form can be very reactive and can interact with biological systems in a large variety of ways. In this regard, a cell presents numerous biologically active metal-binding sites in proteins and nucleic acids. Such adventitious binding is an important chemical mechanism by which exogenous metals exert toxic effects that result in steric rearrangement that impairs the function of biomolecules (Kasprzak, 2002). As discussed above, binding and coordination of essential metals in proteins are critical for enzymatic activity and binding of inappropriate toxic metals in these enzymes are a major mechanism for disrupting normal homeostasis. Mimicry of essential metals provides a major mechanism for toxic metals to produce their effects. In this regard, the toxic metals bind to physiological sites normally reserved for essential elements. The unique physical and chemical properties of essential metals contribute to control and function of a large range of key metabolic and signaling pathways (Kasprzak, 2002; Cousins et al. Through mimicry, the toxic metals gain access to and disruption of the important actions of the essential metal and critical metalmediated cellular functions. For example, mimicry and replacement of zinc is a mechanism of toxicity for cadmium, copper, and nickel. Thallium mimicking potassium and manganese mimicking iron are critical factors in their toxicity. Mimicry of arsenate and vanadate for phosphate allows for cellular transport of these toxic elements, whereas selenate, molybdate, and chromate mimic sulfate and can compete for sulfate carriers and in chemical sulfation reactions (Bridges and Zalups, 2005). Organometallic compounds also act as mimics of biological chemicals, as, for example, with methylmercury, which is transported by amino acid or organic anion transporters (Bridges and Zalups, 2005). Indeed, molecular or ionic mimicry at the level of transport is often a key event in metal toxicity. Metals also induce an array of aberrant gene expression, which, in turn, produces adverse effects. An array of aberrant hepatic gene expression occurs in adult mice after in utero arsenic exposure, which could be an important molecular event in arsenic hepatocarcinogenesis (Liu et al. As discussed, tight coordination of these metals in enzymes catalyzes efficient electron flow and transfer. However, when in excess or unbound, ionic metals catalyze formation of cell membrane damaging oxygen-centered lipid radicals and peroxides, as well as incomplete reduction of molecular oxygen through Haber­Weiss and Fenton reactions with superoxide and H2O2. Chromium is an example of a metal that generates metal and oxygen radical species during reduction from its hexavalent to trivalent form. The results include inappropriate activation of growth or metabolic signaling, loss of essential enzymatic activity, direct structural damage, and if severe, cellular apoptosis and/or necrosis. Disruption of normal cell signaling through inappropriate growth factor signaling, promotion of maladaptive stress responses, and cell senescence can be as detrimental in disease promotion as cell death, especially in chronic diseases such as cancers or cardiovascular disease where there is little or no evidence of cell death. The ability of metals to affect gene expression and generate pathogenic cell phenotypes is well-documented. However, the mechanistic role of metal-induced changes in gene expression in the etiology of human disease has only recently begun to be elucidated. Modern genomic technologies have identified hundreds to thousands of genes whose levels of expression are affected after exposure to excess essential and nonessential metals. The intended consequence of metal activation of gene expression is often to protect the organism from metal-induced damage as metal exposure is associated with increased expression of genes encoding proteins that remove the metal from the cell via chelation or increased export; reduce the level of oxidative stress; and repair the metalinduced intracellular damage. However, the inappropriate activation of gene expression after metal exposure can contribute to a variety of human pathologies. There is no unifying mechanism for metal-activated cell signaling or dysregulated gene expression. However, the activation differs from tightly regulated activation by normal endogenous ligands. The most plausible mechanism for metal activation of receptors and downstream kinases in the receptor signaling pathways is by causing allosteric change through binding to crucial structural cysteine motifs (Ahmadibeni et al. Signal amplification is the inherent property of cell receptors and this allows for a relatively small amount of toxic metal in chronic exposures to affect broad programs of genetic and epigenetic change that ultimately generate pathogenic cell phenotypes. In addition to oxygenbased radicals, damaging carbon- and sulfur-based radicals also occur. In contrast, lower levels of generated lipid and hydrogen peroxides are signal generating and affect gene regulation through protein interactions. However, due to overlapping effects of different metals on the transcriptional programs, it is difficult to predict the cell phenotypes induced by exposure to mixed metals. Likewise, the activity of a single transcription factor can be influenced by a variety of metals through multiple signaling pathways. Metal-induced epigenetic regulation contributes to the overall transcriptional reprograming in metal-induced adaptive and pathogenic responses (Salnikow and Zhitkovich, 2008; Martinez-Zamudio and Ha, 2011; Chervona and Costa, 2012; Ryu et al. The ability of nickel, cadmium, arsenic, and chromium to induce cancer has been linked to metal-inducible epigenetic changes (Arita and Costa, 2009). Factors Impacting Metal Toxicity the standard factors that impact the toxic potential of all chemicals apply to the metals as well. Exposure-related factors include dose, route of exposure, duration, and frequency of exposure. Because metals can be highly reactive, the portal of entry is often initially the organ most affected, as with the lung after hexavalent chromium inhalation. Host-based factors that can impact metal toxicity include age at exposure, gender, and capacity for biotransformation. Fetal-stage toxicity of metals is well-documented, as with methylmercury, and many metals are teratogenic. In addition to overt teratogenic toxicities, fetal and perinatal exposures result in epigenetic reprograming of development that can lead to enhanced risk of adult disease. Developing stem cells, as well as rapidly proliferating and differentiating cells, are important pathogenic (Burris et al. It is quite clear that children are more sensitive to metal intoxication due to developmental stage and continued rapid growth. Due to mimicry, lead exposure is four to five times greater in developing children than adults as they absorb larger amounts of calcium, magnesium, manganese, and strontium to build bones, muscle, and neural tissues. Child pica behavior presents additional exposure concerns as lead and other toxic metals are concentrated in ingested dirt, paint chips, and dusts. Elderly persons are also believed to be generally more susceptible to metal toxicity than younger adults due to overall degeneration of kidneys and other organs involved in metal distribution (Bridges and Zalups, 2017a). Recognition of factors that influence toxicity of a metal is important in determining risk, particularly in susceptible subpopulations. As discussed above, the chemical form and nature of the metals directly affect their toxic potential. The oxidation state and valence of the metal greatly affect its competition for uptake and mechanism of interaction with cellular macromolecules. Metabolism by microbes or mammals affects distribution, site of action, and excretion. For instance, methylmercury is a potent neurotoxin, whereas the inorganic mercurials primarily attack the kidney, and methylated arsenicals are potentially more potent than inorganic arsenic, but are excreted more readily (Bridges and Zalups, 2017b). Lifestyle factors such as smoking or alcohol ingestion may have direct or indirect impacts on the level of metal intoxication. For instance, tobacco smoke contains many toxic metals, such as cadmium and arsenic, and smoking may double the lifetime burden of cadmium in nonoccupationally exposed individuals.

Brevetoxins are produced by the marine dinoflagellate Karenia brevis (formerly known as Gymnodinium breve) (Watkins et al medicine naproxen 500mg generic 3 mg risperidone overnight delivery. Brevetoxins open voltage-gated sodium channels causing uncontrolled Na+ influx into the cell medicine grace potter lyrics 2 mg risperidone buy fast delivery, prolonged depolarization of neuronal and muscle cell membranes symptoms 89 nissan pickup pcv valve bad discount risperidone 3 mg without a prescription, and spontaneous firing treatment zinc overdose cheap risperidone 4 mg with visa. Neurological symptoms include paresthesia (a pricking treatment west nile virus buy generic risperidone 4 mg on-line, tingling sensation), reversal of hot and cold perception, vertigo (false sense of motion), and ataxia (involuntary muscular movement, or spasms). Symptoms typically occur within 30 minutes to a couple of hours after consuming contaminated shellfish and typically resolve within 2 days. The toxicological database for brevetoxins is limited, and comprises only studies on their acute toxicity following intravenous. Because brevetoxins are lipophilic, they pass through cell membranes including the blood­brain barrier. Brevetoxins are rapidly absorbed and distributed throughout the body, and are metabolized in the liver. They are primarily removed in the bile within the first 48 hours, but urinary excretion plays a role after this time as well (Watkins et al. Tetrodotoxin is a potent sodium channel blocker; it reduces the membrane excitability and blocks the conduction of nerve impulse, thereby causing muscle paralysis. Symptoms of toxicity include perioral paresthesia (burning or prickling sensation) that may spread to the entire body, and could be followed by vomiting, lightheadedness, dizziness. In non-fatal poisoning, symptoms usually begin within 30 minutes after exposure and completely resolve within 24 hours after onset. In fatal cases, progression is precipitous, with death due to respiratory muscle paralysis occurring within 6 hours after onset of symptoms. In Japan, puffer fish is a delicacy but it is cleaned and prepared by specially trained chefs. Even though tetrodotoxin is such a potent sodium channel blocker, it cannot block the sodium ion channel of puffer fish because these sodium channels are insensitive to tetrodotoxin. Scombroid poisoning is unique among the seafood toxins because it results from product mishandling rather than contamination from other trophic levels (Hungerford, 2010). It is mostly caused by the consumption of fish (Scombroidae family) with high histamine levels, such as tuna, mackerel, blue fish, sardines, anchovies, and mahi-mahi. Thus, such histamine-induced reactions are often misdiagnosed as IgE-mediated fish allergy. If the fish with high levels of tissue histidine are not refrigerated properly, the bacteria proliferate and convert the tissue histidine into histamine, which is heatstable. Symptoms of toxicity include tingling and burning sensations around the mouth, headache, facial flushing, palpitations, profuse sweating, truncal rash and pruritis, abdominal cramps, nausea, and diarrhea. In most people, these symptoms are self-limiting, but circulatory collapse, shock, and acute pulmonary edema have been described in severe cases (Kerr and Parke, 1998; Becker et al. Because more than 80% of fish consumed in the United States is now imported from other countries, the disease is intimately linked with the global fish trade (Feng et al. Ciguatoxin Ciguatoxin group of toxins include ciguatera toxin, gambiertoxin, and maitotoxin. Gambiertoxin produced by the dinoflagellate is biotransformed by the fish to produce ciguatera toxin. These dinoflagellates are consumed by small herbivorous fishes that are, in turn, consumed by large carnivorous fishes. Ciguatoxins open voltage-gated sodium channels at the neuromuscular junction, resulting in membrane hyperexcitability, spontaneous repetitive neurotransmitter release, blockage of synaptic transmission, and depletion of synaptic vesicles. Maitotoxin is water-soluble and it opens calcium channels of the cell plasma membrane; it is the most toxic nonproteinaceous molecule known (Lehane and Lewis, 2000; Daranas et al. In severe cases the symptoms may begin as soon as 30 minutes after ingestion of contaminated fish, while in milder cases they may be delayed for 24 to 48 hours. Symptoms may last even for months and the administration of mannitol within 24 hours of consumption relieves some symptoms (Dickey and Plakas, 2010). Palytoxin Palytoxin is produced by the zoantharians of the genus Palythoa (cnidarians found in coral reefs). Fishes and crabs living in close association with or eating this mass may become contaminated with palytoxin. Palytoxin has been reported in mackerel, parrotfish, and several species of crabs. Within several hours, symptoms include myoglobinuria, a burning sensation around the mouth and extremities, muscle spasms, paresthesia, bradycardia, dyspnea (labored breathing), and dysphonia (difficulty in speaking). Some Microbial Contaminants in Food Food-related illnesses resulting from microbial contamination can pose a serious threat to public health. However, the actual frequency may be significantly higher because (1) an outbreak is classified as such only when the source can be identified as affecting two or more people and (2) most home poisonings are mild or have a long incubation time and are therefore not connected to the ingested food, and go unreported. Exotoxins are not an integral part of the bacterial membrane; they are soluble, usually heat-labile proteins found in the cytoplasm, and are easily secreted into the surrounding medium, usually by gram-positive bacteria. Exotoxins enhance bacterial virulence, and are further subdivided according to their mode of action, such as emetic toxins that trigger severe vomiting; enterotoxins that cause diarrhea; cytotoxins that kill host cells; neurotoxins that interfere with normal transmission of nerve impulse. Table 27-10 lists some important foodborne bacterial exotoxins and their mode of action in causing toxicity. Endotoxins are not secreted but released from dead or dying gramnegative bacteria. Humans have background exposure to endotoxins by the oral and inhalation route, which may vary significantly depending on the living and working conditions (Madsen, 2006; Inagawa et al. Stimulation of the afferent vagal neurocircuit triggers the vomiting center in the hindbrain Stimulates the efflux of ions and water from intestinal epithelial cells. Binds to the claudin receptors (tight junction membrane proteins) on enterocytes, forms large complex that forms pores in the membrane, causes a strong influx of calcium, and apoptotic cell death. The same mechanism is also utilized by ricin in castor beans Interferes with normal transmission of nerve impulse by blocking neurotransmitter. The information provided in the book is abbreviated and general in nature, and is intended for practical use. In the following narrative, a few of the microbial contaminants in food are briefly discussed. Foods associated with botulinum toxin include improperly canned low-acid foods. An increasing source of poisonings is from the use of flavored oils or oil infusion, most typically in garlic-in-oil preparations. All Clostridia are gram-positive, spore-forming anaerobes, and they produce a total of seven serotypically and antigenically distinct botulinum neurotoxins (serotypes A­G) (Rossetto et al. Botulinum toxin is neurotoxic that interfere with neural transmission by blocking the release of acetylcholine at peripheral nerve endings, causing muscle paralysis. Clinical illness is characterized by cranial nerve palsies, followed by descending flaccid muscle paralysis, which can involve the muscles of respiration. The toxins are heat-labile (may be rendered harmless at 80°C to 100°C for 5 to 10 minutes) but the spores are among the most heat-resistant. Current methods for detecting botulinum toxin include a mouse bioassay and an enzyme-linked immunosorbent assay, with the mouse bioassay being the accepted standard. Virtually all food poisoning is produced by type A strain, although a particularly severe form (a necrotic enteritis called "pig-bel" among indigenous peoples of the New Guinea highlands or in Germany known as "Darmbrand") is produced by the type C strain, which has a mortality rate of 15% to 25% even with treatment. The toxin is normally trypsin-sensitive, but people with low intakes of protein or who consume trypsin-inactivating foods. This is manifested by abdominal cramping and diarrhea; diarrhea occurs within 8 to 16 hours. The emetic toxin (a cyclic oligopeptide) is pre-formed in food, and the enterotoxins (proteins) are produced in the small intestine of the host (Granum and Lund, 1997). The emetic thermostable toxin (surviving 259°F for 90 minutes) is called cerulide (a small cyclic peptide, 1. The diarrheagenic thermolabile toxin (surviving 133°F for 20 minutes) is produced by serotypes 1, 2, 6, 8, 10, and 19 and may also be produced in situ in the lower intestine of the host. The diarrheal form may actually consist of three toxins, one of which is hemolytic (Granum, 2006). Foods associated with this organism and its toxic properties include boiled and fried rice (principally the emetic form), while the diarrheal form has a wider occurrence and may be found in meats, stews, pudding, sauces, dairy products, vegetable dishes, soups, and meat loaf (Granum and Lund, 1997; Crane, 1999). The foods associated with the two types somewhat reflect the geographic distribution of the types. For example, the emetic type predominates in Japan, whereas in North America and Europe, the diarrhea type is most often seen. Evidence is accumulating that other species of Bacillus may elaborate food toxins, including B. This has been approved for addition to swine, bovine, poultry, and rabbit feed in the European communities (Kotsonis and Burdoch, 2013). Staphylococcus aureus Staphylococcal intoxication includes staphyloenterotoxicosis and staphylococcus food poisoning. Sources of Staphylococcus include nose and throat discharges, hands and skin, infected cuts, wounds, burns, boils, pimples, acne, and feces. Other reservoirs include mastitis in the udders of cows and ewes (responsible for contamination of unpasteurized milk) and arthritic and bruised tissues of poultry. Foods usually are contaminated after cooking by persons cutting, slicing, chopping, or otherwise handling them, and then keeping them at room temperature for several hours or storing them in large containers. Foods associated with staphylococcal poisoning include cooked ham, meat products including poultry and dressing, sauces and gravy, cream-filled pastry, potatoes, ham, poultry, fish salads, milk, cheese, bread pudding, and generally high-protein leftover foods (Kotsonis and Burdoch, 2013). Hence, most outbreaks in the United States have been associated with hamburgers and other beef products, although raw vegetables (often fertilized with manure) and unpasteurized apple cider and juice have been reported as sources of outbreaks. Outbreaks in Europe are more often associated with contamination of recreational waters (swimming pools, lakes, etc. Other sources of contamination include person-to-person contact (especially in families and among institutionalized persons) and contact with farm animals especially following educational farm visits (Karch et al. Contamination of food by unhygienic food handlers and consumption of raw vegetables raised in contaminated soils are two main contributors to the incidence of Shigella diarrhea. Food products can be contaminated by contact with soil, feces, discharges, and urine from infected animals and humans. Listeria can also live in food processing plants and contaminate a variety of processed foods. Listeria can grow even in the refrigerator, but is killed by cooking and pasteurization. Listeriosis in pregnant women can result in abortion, fetal death, or premature birth. Listeriosis has a low incidence of infection, although this is undeniably increasing, with a high fatality rate among those infected (Mateus et al. Since 2008, several Listeriosis outbreaks have been linked to diverse types of fresh produce: sprouts, celery, cantaloupe, stone fruit, and apples. The 2011 cantaloupe-associated outbreak was one of the deadliest foodborne outbreaks in recent U. In the recent past there have been multiple reports of food-related Listeria outbreaks in the United States. Consuming contaminated food causes nausea, vomiting, abdominal cramps, diarrhea, fever, and headache. The interval between exposure and the onset of the symptoms may be as short as a few hours or it can take a couple of days. The illness is generally self-limiting for people with intact immune system and is resolved within a week. Mortality is rare but occurs in the very young and the very old and in immunocompromised individuals (Coburn et al. In the recent past there have been several multistate foodborne outbreaks involving Salmonella. This bacterium is an emerging opportunistic pathogen that is associated with rare but life-threatening cases of meningitis, necrotizing enterocolitis, and sepsis in premature and full-term infants. Some Foodborne Molds and Mycotoxins Molds have served humans for centuries in the production of foods. Frank growth of fungi on animal hosts produces mycoses, whereas dietary, respiratory, dermal, and other exposures to toxic fungal metabolites produce mycotoxicoses. In the context of food toxicology, a discussion of mycotoxins and the mycotoxicosis they cause is more relevant. Mycotoxins represent a diverse group of chemicals that can occur in a variety of plants used as food, including commodities such as cereal grains (barley, corn, rye, wheat), coffee, dairy products, fruits, nuts, peanuts, and spices. A few mycotoxins also can occur in animal products derived from animals that consume contaminated feed. However, because commodities are consumed in great amounts, the mycotoxins present in these foods represent the greatest risk (Cousins et al. Data from animal studies indicate that the consumption of food contaminated with mycotoxins has the potential to contribute to a variety of human diseases (Miller, 1991). Importantly, the presence of a toxigenic mold does not guarantee the presence of a mycotoxin, which is elaborated only under certain conditions. Although there are many different mycotoxins and subgroups (Table 27-11), this discussion will focus on aflatoxins, trichothecenes, fumonisins, ochratoxin A, and ergot alkaloids. Epidemiological studies conducted in Africa and Asia suggest that it is a human hepatocarcinogen, and various other reports have implicated the aflatoxins in incidences of human toxicity. Aflatoxin B1 is the most potent natural carcinogen known and is the major aflatoxin produced by toxigenic strains (Bennett and Klich, 2003). Generally, aflatoxins occur in susceptible crops as mixtures of aflatoxins B1, B2, G1, and G2, with only aflatoxins B1 and G1 demonstrating carcinogenicity. Aflatoxins may occur in a number of susceptible commodities and products derived from them, including edible nuts (peanuts, pistachios, almonds, walnuts, pecans, and Brazil nuts), oil seeds (cottonseed and copra), and grains (corn, grain sorghum, and millet). The two major sources of aflatoxin contamination of commodities are field contamination, especially during times of drought and other stresses, which allow insect damage that opens the plant to mold attack, and inadequate storage conditions. Aflatoxin B1 is also highly mutagenic, hepatocarcinogenic, and possibly teratogenic.

The extracellular and intracellular concentrations of all of the essential metals are tightly controlled by their transporters and chaperone proteins such that these proteins become rate-limiting regulators of metal action and toxicity treatment yellow jacket sting discount risperidone express. Many of the transporters are promiscuous in transporting a number of similarly sized and valenced cations silent treatment purchase risperidone 3 mg free shipping. This provides an axis for nonessential symptoms zenkers diverticulum order risperidone 3 mg with visa, toxic metals to have cellular access and opportunity to cause toxicity my medicine order risperidone from india. Toxicity also occurs when toxic metals or excessively high concentrations of essential metals outcompetes an essential metal for transport and action symptoms quitting smoking purchase generic risperidone on-line. For example, elemental nickel will cause cardiotoxicity when the nickel is in sufficient concentration to block calcium from entering the cardiomyocytes through L-type channels. In contrast, metal transporters are also important for cellular resistance to metals or metalloids (Rosen, 2002). For instance, enhanced efflux via multidrug resistance protein pumps limits arsenic toxicity and is involved in acquired tolerance to arsenic (Liu, 2010). Decreased influx via reduced calcium G-type channels is involved in acquired tolerance to cadmium (Leslie et al. A full review of metal transporter and channel biology is beyond the scope of this chapter, and examples of their importance to metal toxicity are discussed for the individual metals. Metal ions are rarely free during distribution and transport, because free metal is reactive. Thus the free concentration is tightly regulated to provide appropriate homeostasis and desired function. Metal chaperones are a class of proteins and small molecules that prevent metal ions from roaming freely within the circulation and in cells. Transferrin is a glycoprotein that binds most of the ferric iron in plasma and helps transport iron across cell membranes where it is delivered to ferritin, the primary cellular iron storage protein. Transferrin also transports aluminum and manganese and may serve as a general metal detoxicant protein, because it binds many toxic metals including cadmium, zinc, beryllium, and aluminum. Other components of tobacco smoke may also influence pulmonary effects, as, for instance, with metals that are lung carcinogens or promote pulmonary disease. Arsenic exposures synergize with tobacco smoke to increase risk of cardiovascular and lung disease, as well as cancer (Parvez et al. Alcohol ingestion may influence toxicity by altering diet, reducing essential mineral intake, and altering hepatic iron deposition. Alcohol can also synergize with metals, such as arsenic, through amplification of interacting signal transduction pathways (Klei and Barchowsky, 2008) that may promote cancers (Wang et al. The composition of the diet can significantly alter gastrointestinal absorption of various dietary metals. In addition, susceptibility to the toxic effects of metals can be altered by dietary constituents competing at sites of metal action. Adaptive mechanisms are critical to susceptibility to the toxic effects of metals, and organisms have a variety of ways in which they can adapt to otherwise toxic metal insults. Typically, adaptation is acquired after the first few exposures and can be long-lasting or transient after exposure ceases. Adaptation can be at the levels of uptake and excretion or, with some metals, through long-term storage in a toxicologically inert form. For instance, enhanced arsenic efflux is involved in acquired tolerance to the metalloid on the cellular level (Liu et al. These bodies are thought to be protective by limiting the level of free, and therefore toxic, lead within the cell, and the inability to form such bodies clearly increases the chronic toxic effects of lead, including carcinogenesis (Waalkes et al. Metal exposure can also induce a cascade of molecular/genetic responses that may reduce toxicity, such as with metal-induced oxidative stress responses (Valko et al. It is clear that acquired metal adaptation, although allowing immediate cellular survival, may in fact be a potential contributing factor in long-term toxicity (Waalkes et al. For instance, acquired self-tolerance to cadmium- or arsenic-induced apoptosis may actually contribute to eventual carcinogenesis by allowing survival of damaged cells that would otherwise have been eliminated (Hart et al. Therapeutic use and Toxicity of Metals Metals and metal compounds have a long and rich history of pharmacological use. Metallic compounds, largely because of their potential toxicity, have been used in chemotherapeutic settings for millennia. Traditional Chinese medicines, usually complex mixtures, were made with toxic metals, such as mercury, as intentional ingredients (Liu et al. Arsenicals were the workhorse therapeutic agents of the 1800s, although they caused as many untoward effects as cures. Inorganic arsenic trioxide remains a frontline drug for treating promyelocytic leukemia (Chen et al. Today, many metallic chemicals remain valuable pharmacological tools, as exemplified by the highly effective use of platinum compounds in cancer chemotherapy. Other examples of medicinal metals used today include aluminum (antacids and buffered analgesics), bismuth (peptic ulcer), lithium (mania and bipolar disorders), and gold (arthritis). Metallic compounds find their way into a variety of pharmacological preparations as active or inactive ingredients. Treatment of metal poisoning is sometimes used to prevent, or even attempt to reverse, toxicity. Metal chelation has made a resurgence in the treatment of cardiac diseases (Solenkova et al. Most chelators are not specific and will interact with a number of metals, eliminating more than the metal of concern and possibly essential metals. Metal chelation therapy should be considered a secondary alternative to toxic metal exposure reduction or even prevention. Chelator therapy can be used for many different metals including lead, mercury, iron, and arsenic. Arsenic exists in the trivalent and pentavalent forms and is widely distributed in nature. The most common inorganic trivalent arsenic compounds are arsenic trioxide and sodium arsenite, while common pentavalent inorganic compounds are sodium arsenate, arsenic pentoxide, and arsenic acid. Important organoarsenicals include arsanilic acid, arsenosugars, and several methylated forms produced as a consequence of inorganic arsenic biotransformation by various organisms, including humans. Industrial and military toxic arsenicals include phenylarsine oxide, roxarsone, and lewisite. Occupational exposure to arsenic occurs in the manufacture of pesticides, herbicides, and other agricultural products. Exposure to arsenic fumes and dusts occurs in smelting industries, especially copper smelting (Enterline et al. Food, especially seafood and rice, may contribute significantly to daily arsenic intake (Carlin et al. The word arsenic is from the Persian word Zarnikh, as translated to the Greek arsenikon, meaning "yellow orpiment. The element was first isolated in about 1250, but arsenicals Toxicokinetics Inorganic arsenic is well absorbed (80% to 90%) from the gastrointestinal tract, distributed throughout the body, often metabolized by methylation, and then excreted primarily in urine (Hughes et al. Trivalent inorganic arsenic and trivalent methylated metabolite absorption from the gastrointestinal track and movement into cells throughout the body occur through aquaglyceroporins 7 and 9 (Liu, 2010). As these channels are primarily water and glycerol channels, trivalent arsenicals can freely distribute throughout the body with the volume of distribution of water. Pentavalent inorganic and methylated arsenic species resembles phosphate and must compete with mM amounts of phosphate for cell entry. The whole-body biological half-life of ingested arsenic is about 10 hours, and 50% to 80% is excreted into the urine over 3 days (Kenyon et al. The biological half-life of methylated arsenicals is in the range of 30 hours (Hughes et al. Arsenic has a predilection for skin and is excreted by desquamation of skin and in sweat, particularly during periods of profuse sweating. Arsenic in the fingernails and hair has been used as a biomarker for exposure, including both current and past exposures, while blood and urinary arsenic is a good indicator for current exposure. Some animal species even lack arsenic methylation capacity, perhaps as an adaptation mechanism. Arsenate (As5+) is rapidly reduced to arsenite (As3+) by arsenate reductase (presumably purine nucleoside phosphorylase). However, large variations in arsenic methylation occur due to factors such as age and sex. Approximately 30% of patients undergoing arsenic chemotherapy experience life-threatening re-entrant arrhythmias caused by arsenic impairment of cardiac inwardly rectifying potassium channels (Ficker et al. Arsenic cancer therapies are also associated with noncardiogenic pulmonary edema and severe pulmonary leukocytosis (Camacho et al. Arsine gas, generated by electrolytic or metallic reduction of arsenic in nonferrous metal production, is a potent hemolytic agent, producing acute symptoms of nausea, vomiting, shortness of breath, and headache accompanying the hemolytic reaction. Exposure to arsine is fatal in up to 25% of the reported human cases and may be accompanied by hemoglobinuria, renal failure, jaundice, and anemia in nonfatal cases when exposure persists (Pullen-James and Woods, 2006). Symptoms of acute intoxication include fever, anorexia, hepatomegaly, melanosis, cardiac arrhythmia, and, in fatal cases, terminal cardiac failure. Acute arsenic ingestion can damage mucous membranes of the gastrointestinal tract, causing irritation, vesicle formation, and even sloughing. Sensory loss in the peripheral nervous system is the most common neurological effect, appearing at 1 to 2 weeks after large doses and consisting of Wallerian degeneration of axons, a condition that is reversible if exposure is stopped. Anemia and leucopenia, particularly granulocytopenia, occur a few days after high-dose arsenic exposure and are reversible. In humans, chronic exposure to arsenic induces a series of characteristic changes in skin epithelium. Susceptibility to skin lesions is increased by folic acid and vitamin B deficiencies due to impaired methylation of ingested inorganic arsenic (Gamble et al. Cardiovascular disease and coronary artery disease in particular are the noncancer diseases most strongly associated with environmental arsenic exposures (Moon et al. Several highly powered prospective epidemiological studies have confirmed the association even with low to moderate levels of arsenic exposure (Chen et al. The dominant form of disease stems from the atherogenic potential of arsenic and its propensity to enhance both vessel disease and prolongation of the cardiac Q-T interval (Chen et al. Atherosclerotic mouse models have shown increased atherosclerosis after even moderate arsenic exposures and that smooth muscle cell remodeling and macrophage lipid metabolism are the prime pathogenic targets (Lemaire et al. In addition, mouse models have also demonstrated that low to moderate levels of exposure cause perivascular fibrosis and loss of perivascular matrix integrity, especially in the heart (Soucy et al. Peripheral vascular disease has been observed in persons with chronic exposure to inorganic arsenic in the drinking water in Taiwan (Wang et al. Studies have shown an association between high arsenic exposure in Taiwan and Bangladesh and an increased risk of diabetes mellitus (Navas-Acien et al. Finally, the vascular endothelium is highly sensitive to arsenic exposures with low-level exposure promoting proliferation, angiogenesis, and vessel remodeling, whereas high exposures cause cell death and loss of vessels (Soucy et al. Susceptibility to the respiratory effects of arsenic is enhanced by in utero exposure (Rahman et al. In addition, arsenic exposure is associated with increased respiratory tract infections (Rahman et al. Animal studies suggest that low to moderate levels of arsenic in utero exposures of mice to low to moderate concentrations decrease immune gene expression and promotes inflammatory protein expression (Kozul et al. In keeping with reduced lung defenses, as in the heart, arsenic compromises lung matrix, wound repair, and barrier function (Hays et al. Liver injury, characteristic of long-term or chronic arsenic exposure, manifests itself initially as jaundice, abdominal pain, and hepatomegaly (Mazumder and Dasgupta, 2011). Liver injury may progress to cirrhosis and ascites, even to hepatocellular carcinoma (Liu and Waalkes, 2008; Straif et al. This neuropathy usually begins with sensory changes, such as numbness in the hands and feet, but later may develop into a painful "pins and needles" sensation. Both sensory and motor nerves can be affected, and muscle tenderness often develops, followed by weakness, progressing from proximal to distal muscle groups. Arsenic exposures, especially in utero and during early developmental exposures, also impair central cognition and memory behaviors (Wasserman et al. In addition, studies in mice suggest that the impact of in utero and perinatal exposures on cognition may be less in females who respond to arsenic with greater antioxidant adaptation (Allan et al. As mentioned above, this immunosuppressive potential is prevalent in respiratory tract infections (Kozul et al. For example, arsenic exposures alter transcriptional programing in circulating macrophages to enhance atherogenesis that underlies arsenic-promoted cardiovascular disease (Lemaire et al. In addition to increasing inflammation, arsenic may increase allergy and autoimmune diseases (Ferrario et al. Further impacts on the circulation include hematologic consequences of chronic exposure to arsenic that interferes with heme synthesis and increase in urinary porphyrin excretion, a biomarker for arsenic exposure (Ng et al. Pentavalent arsenate mimics phosphate and can inhibit phosphotransfer reactions, such as mitochondrial oxidative phosphorylation, when present in concentrations that are stoichiometrically competitive. In addition to these basic modes of action, several mechanisms have been proposed for arsenic toxicity and carcinogenicity. Transition between trivalent and pentavalent oxidation states occurs through two electron transfer and thus arsenic is not capable of directly generating reactive oxygen species. The oxidants generated are second messengers in signal transduction cascades leading to activation of tyrosine and serine/threonine kinase pathways for enhanced proliferation, cell turnover, and potential transformation (Simeonova and Luster, 2002; Andrew et al. Some mechanisms, however, may be cell type or organ specific, as there is emerging evidence that arsenic impacts target tissue stem cells in various ways to facilitate oncogenic change or impair tissue metabolism and regeneration (Tokar et al. The mode of action for arsenic-induced cancers remains unresolved and is likely to be multifactorial.

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